Indoor VHF BDA Antenna needed with 18 MHz BW, low end at 138

[ChrisHaz]

Does Motorola make indoor VHF BDA antennas? I need some which have about 18 MHz of bandwidth between the receive and transmit splits. The low end at 138 MHz, high end at 156 MHz. If not Motorola, anyone?

[escomm]

Last I checked Motorola makes no antennas

They take antennas from various manufacturers and put their name on it

Or they just charge for the gear like it was their name on it

[Will]

Comtelco EDX150

[ChrisHaz]

Thank you, I checked the Comtelco EDX150 antenna and it looks great for the outdoor end, but not the indoor end of the BDA system which will require a dozen or so of them in a distributed antenna system spread throughout the basement of a large building. Another requirement is plenum fire rating for public safety systems, will likely need to be in some kind of radome, unfortunately, unless hidden above ceiling tiles.

[ChrisHaz]

What I meant by unless hidden, is that the aesthetics of the EDX150 isn't suited for basement office installation, something with a radome or which can be hidden (if ugly) is what I am forced to use. Both types would still need to be fire rated/NFPA.

[RFguy]

You won't get that type of bandwidth on a standard radome type antenna (such as a railroad antenna). You'll only get 3 to 4 MHz BW.

Systems we've installed in the past needed about 14 MHz in lower VHF (140 to 154). We used 1/4 wave wideband mobile type antennas mounted on a ground plane. The whip is around 24" long though.

We have had to resort to the Comtelco EDX150 type (we used Sinclair SD210). We cut down the mast and hung them on a bracket from the ceiling. We had radomes fashioned at a plastics fabricator.

[Bill_G]

Your only other choice is to use rubber duckies. Try to keep them out in the open, and not buried in the interstitial.

[ChrisHaz]

Thank you for your feed back and recommendations. I've been looking at a railroad antenna built by Comprod communication, their model 357-75 has 8 MHz bandwidth, but full bandwidth; 17.7 MHz is what I need, with a VSWR of 3:0 in the end of the band I choose, if we bought them. I'm thinking I can have it made so the transmit of the BDA is the resonant side, siding it up towards the receive side as a compromise and having that 3:0 or 25 percent mismatch on the receive end. I think this would be more efficient than using wide bandwidth rubber duckies, what do you think? One of my constraints is using NFPA fire rated equipment, I could probably get a sign off on using something else for the antenna but am looking for a solution which will allow me to use fire rated.

I would be very interested in your thoughts, only thing about the rail road antenna, it requires a 14 x 14 inch ground plane.

[RFguy]

Comprod spec sheet shows that antenna has a 3 MHz bandwidth (1.5:1 VSWR) or 5 MHz for a 2.0:1 VSWR.
http://www.comprodcom.com/Products/Tran ... hz_25__95/

One thing I found with Comprod is their specs are "optimistic", where Sinclair's specs are "realistic"

[Bigred]

Installed a VHF EMR bda and used their antennas which are nothing more than a half wave dipole, however a lot more low profile than the above suggestions. Model I believe is B2H3/Q5BM. Funny though, couldn't find specs on it from EMR's website but the UHF b/w is listed as 20 mhz so maybe about half that?

[RFguy]

The UHF version (B2K3/Q5BM) is listed as 10 MHz in the spec sheet. VHF would be 1/3 that.

TheUHF version, B2H3/Q5BM is listed as having a 4 MHz bandwidth.

Been there, done that. Even made our own with wideband whips. No luck improving on the bandwidth.

[ChrisHaz]

Thank you for your help, I now see the 357-75 has 4 MHz of BW, my bad, I don't know where I got the 8 MHz now. I like the low profile idea of the dipole if a balun is on it. When I was a high school ham radio operattor I used to build wide band dipoles by putting different radiators in parallel that had shorter and longer lengths from the middle desired resonance, they were inches apart and joined on each side of the middle insulator. They worked, maybe we could do something like that for this but then it isn't a fire certified UL listed antenna that I'm being told by my PM we need for public safety systems. Anyone ever get a sign off from a fire martial or other for a non-certified antenna for use in a BDA system?

[ChrisHaz]

I could make a dipole out of aluminum rods with three elements on each side of different lengths and get the bandwidth that way, but then it isn't UL approved or fire rated etc., if anyone has installed a shop manufactured antenna, were you able to get a waiver of some kind from your fire marshal or other? Better than doing this I think the earlier suggestion of using a Sinclair SD210 138-174 MHz folded dipole would be the thing to do and cheaper but getting it approved is my next challenge.

[VE3HKB]

Finding a wideband VHF fire-rated antenna may be difficult, but not impossible (think mining).
There may be a much simpler solution for you - leaky coax. Already made in fire and plenum rated versions, in a number of frequency ranges.
While more expensive than similar non-radiating cables, once you subtract the cost of antennas, I think you'll find it a better solution. Simpler installation (no antennas to mount).

[ChrisHaz]

I was considering leaky coax, but the building we will be installing the system is built like a prison, in fact, has jail cells in it. All concrete, lots of steel doors and sheet metal in some areas. My understanding is leaky coax is good for hallways and offices but doesn't work well when needing to cover areas which are several thick walls away. What do you think?

Thanks

[ChrisHaz]

It appears the problem is solved, a company called Fractenna can make them for us in a monopole configuration which includes not only 138-156 MHz, but 769-805 MHz in one antenna too. They use 3D printers, three week lead time. They can make fire rated radomes too, but it takes longer for those. All of these will be hidden above drop down ceilings.